1. Field of the Invention
The invention is directed to an improved a fuel injection valve for internal combustion engines.
2. Description of the Prior Art
A fuel injection valve of the type with which this invention is concerned is known from WO 96/19661. A fuel injection valve of this kind contains a valve needle that can slide in the longitudinal direction in a bore; the combustion chamber end of the bore is provided with a conical valve seat. The valve needle is guided in a section oriented away from the combustion chamber and, between the wall of the bore and the section of the valve needle oriented toward the combustion chamber, a pressure chamber is formed, which can be filled with highly pressurized fuel. The pressure chamber here extends to the valve seat, which is conical and contains at least one injection opening. At the end oriented toward the valve seat, the valve needle has an essentially conical valve sealing surface so that when the valve sealing surface is lifted away from the valve seat, fuel can flow from the pressure chamber, between the valve seat and the valve sealing surface, and to the injection openings. The valve needle is acted upon by a closing force that presses the valve sealing surface against the valve seat and, in the absence of other forces, prevents fuel from being injected through the injection openings.
The valve sealing surface has a first conical region whose opening angle is smaller than the opening angle of the conical valve seat. Downstream of the first conical surface in the flow direction of the fuel, the valve sealing surface has another conical surface whose opening angle is greater than the opening angle of the valve seat. Between the two conical surfaces of the valve sealing surface, an annular groove is formed, which extends in a radial plane of the valve needle and borders on both conical surfaces.
In order to inject fuel into the combustion chamber of the internal combustion engine, highly pressurized fuel is conveyed into the pressure chamber of the injection valve. As a result, a valve needle pressure surface and part of the valve sealing surface are subjected to a hydraulic force that acts in opposition to the closing force. If the closing force is reduced, then the hydraulic forces move the valve needle away from the valve seat so that fuel can flow into the injection openings. The hydraulic pressure generated by the fuel pressure in the pressure chamber acts on the entire cross section of the valve needle when it is open. In order to overcome this force, the closing force must be correspondingly high since modern fuel injection systems require short closing times of the fuel injection valve in order to permit rapid sequences of precisely metered injections. As soon as the valve needle comes back into contact with the valve seat, this eliminates the hydraulic pressure on part of the valve sealing surface so that there is then a powerful excess of closing force in relation to the hydraulic force on the valve needle. This means that the valve needle is pressed against the valve seat with a large amount of force, which leads to increased wear at this point over time and can significantly reduce the service life of the fuel injection valve. Particularly in the newest fuel injection systems that operate with pressures of up to 200 MPa, the materials are being pushed to the limits of their load capacities.